1. Field of the Invention
This invention relates to the preparation of novel heterocyclic compounds and compositions containing them and is more particularly concerned with the preparation of N-isocyanatoalkanoyl-substituted cyclic ureas, with the preparation of stable one-component polyurethane-forming systems and with processes for preparing polyurethanes therefrom.
2. Description of the Prior Art
One-can systems (actually blends of two or more components), which are storage stable but which can, at any required time, be converted to polyurethanes, are well-known, particularly in the coating art; see, for example, Saunders and Frisch, Polyurethanes: Chemistry and Technology, Part I (pp 8 and 118-121), 1963 and Part II (pp 453-454), 1964, Interscience Publishers, New York, N.Y. Such systems generally comprise a blocked polyisocyanate and a polyol. Upon heating the mixture the blocked isocyanate groups are liberated and react with the polyol to form the polyurethane. The disadvantage of such systems is that the blocking agent (phenol, caprolactam or like agents) which is liberated in the heating process can remain trapped in the resulting resin, which can have deleterious results as far as properties of the resin are concerned, or escape as a gas which may give rise to problems of possible toxicity.
Compounds have recently been described which contain blocked isocyanate groups in the form of cyclic ureas which, upon heating, give rise to diisocyanates without liberating any blocking agent, the process being simple ring opening of the cyclic urea group; see U.S. Pat. Nos. 4,138,398; 4,190,599; 4,217,436 and 4,349,663.
We have now found that certain novel compounds, which contain one free iscoyanate group and one blocked isocyanate group in the form of a cyclic urea group, possess particular advantages in the preparation of "one-can" polyurethane systems with particular reference to such systems for use as coating compositions.